Hardenability test



De@ 16 l941 w. E. JoMlNY 2,266,322

' HARDENABILITY TEST Filed Aug. 21, 1939 Patented Dec. 16v, 1941 HARDENABILITY TEST Walter E. Jominy, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a

' corporation of Delaware Application August 2*'1, 1939, seria1No.291,149

(Cl. 'z3-51) 5 Claims.

This invention relates to a hardenability test for determining the ability of a steel to harden to a depth below the surface.

There are many uses for a test to determine the hardness characteristic of a steel and the primary object of the present invention is an improved hardenability test which is much simpler and more practical than tests heretofore used for this purpose and which may be applied to either carburized steels or steels that are not carburized. Other objects and advantages of the present invention will become more apparent from the following detailed description of an embodiment of the invention.

In brief, the present invention comprises the hardening of an' elongated test specimen of suitable size land shape by heating the same above the critical temperature of the steel to the desired hardening temperature and cooling the specimen by extracting heat from one end of the specimen. This is done preferably by a jet of cooling Water which is forced into contact with one end face only of the specimen.vv After the.

sample is cooled hardness readings are Athereupon taken at various intervals along the length of the bar and the hardenability characteristics of the test piece ascertained. The-greater the distance from the water cooled end at which the hardness x is above a standard, the'better the characteristic of the steel as regards depth hardening.

Reference is herewith made to the accompanying drawing, in which:

end face of the specimen is deflected and runs into the tank.

In the pipe I4 is a suitable pressure regulating valve I8 and a quick opening valve 20. In a branch line 22 leading from the pipe I4 is a third valve 24. 'I'he purpose of the three valves is as follows:

Before operating the device the valve I 8 will be adjusted to cause a suitable Jet of Water to be formed. In ordinary practice, this valve is so adjusted that the jet of water will extend upwardly approximately 21/2" from the end I5 of the pipe I4 when no test specimen is in cooling position and when the quick'opening valve is in open position. 'I'he size and shape of the jet of water must be such that no water will strike the sides of the specimen. Valve 20 is a quick opening valve which is normally closed but which in the operation of cooling the test specimen is rapidly opened by the operator after the heated 'test specimen has been placed in position. Valve 24 is provided in order that a certain amount of water in the tank can be pumped outof the tank at the conclusion of a cooling operation by means of the pump I0 and replaced by cooler water so that the Water in the tank at the -beginning of Figure 1 is an elevational view of an apparatus for cooling a heated test specimen by forcing a jet of cooling water into contact with one end face only.

Figure 2 is a fragmentary view substantially on a `line 2--2 of Figure 1.

Figure 3 is a modified form of test bar which may be used in place of that shown in Figure 2. In the vdrawing is shown a tank 2 adapted to have a supply of water therein and mounted upon a suitable platform 4 having rollers 6 6 whereby` the apparatus may be readily moved from place to place. Near the bottom of the tank is a water line 8 leading to the intake side of a water pump I0 which is driven by any suitable means such as an electric motor I2. A water pipe I 4 leads from the discharge or high pressur side of the pump and has an upwardly extending discharge end or nozzle I5 disposed adjacent the top of the tank. In this way the water pump causes water to be forced upwardly into contact with the lo'wer end of a suitable test specimen I6 as best shown in the next cooling operation is at standard temperature. A temperature of '15 F. is usually used. It will be understood that valve 24 is closed during the cooling operation and is opened when it is desired to pump water out of the. tank.

The fixture for supporting the test sample of the desired analysis in the hardening or cooling operation comprises a Cshaped member 26 supported by a strap or bracket. member 284, which in turn is fixed to a point near the free'or open end of the pipe I4'by means of a clamp 30. The test specimen is supported in the xture by meanslof an adapter 32 having a head 34 and a screw threaded end 36, the latter being in lscrew-- threaded engagement with the upper end of the test` specimen I6. The adapter is provided to support the test specimen in position above the nozzle and permits handling in away such that Y the heated test bar need not be engaged by the tongs or'other apparatus used by/thepperator in noving the test sample from the furxace to the quenching position. When in cooling position the lower end of the specimen is 1/2" from the open end of the pipe "I4.

In the form shown in Figure 2 the test bar is 1" in diameter and 2%" long. The lower face vis a plane surface as shown. With the .iet of water as described the water will contact the entire end Figure 2. The cooling water after striking the 55 face only of the bar.

In Figure 3 is shown a slightly different form of test specimen i6 which may be used in place of that shown in Figure 2. In Figure 3 the test bar or specimen is. 1" in diameter as in the form of Figure 2 but the bar is slightly longer to provide a skirted portion d0. `In either of the forms shown the cooling medium is brought into contact with the end face only of the test bar so that all of the cooling must take place from this end. It is important that the water contact the entire end surface only and not the sides of the test specimen.

It will be understood that other sizes and shapes of test bars may be used in place of those shown and described.

In order that the temperature of the cooling water. in the tank remain at nearly a constant value during the cooling operation it is desirable that the tank be comparatively large. With a tank 131/2" in diameter and about 21/2 feet high nearly llled with water at 75 F. it has been found that` the temperature will rise about one degree F. in cooling from 1700" F. one of the test specimens of the rsize above described. A temperature rise on this order gives satisfactory results. In place of a temperature of 75 F. of the cooling medium at the start of a cooling operation other temperatures may be used. In order to carry out the cooling under similar conditions in each instance it is important that the temperature of the cooling medium be at the same temperature in each case.

After the bar has been thoroughly cooled, the bar and adapter are removed from the fixture. The hardness of the bar is then measured at various intervals from the .water cooled end. A deflnite standard of hardness is set and the distance from the water cooled end at which the hardness is at least as high as the standard is given as the hardenability characteristic of the steel under test. i

When the hardness characteristics of a carburized steel are to be determined the test specimen is made of the kind of steel to be tested and the adapter screwed into the end thereof. The specimen and adapter are then carburized eight hours at 1700" F.y removed from the carburizing box and cooled by spraying Water on one end face only as described. After the sample is cooled it is polished with emery paper and the hardness measured at various points from the Water cooled end to the adapter end. After this is done a strip of metal .015 is removed by grinding and another series of hardness readings is made. From the tWo readings the hardness characteristics of the steel being tested are ascertained.

With steels that are not carburized it has been found desirable to make hardness readings at .015 inch below the surface of the bar in order to make certain that the hardness readings are not taken' on portions of the test specimen that may possibly havebeen decarburized. This may be accomplished by grinding a at .015" deep along the entire length of the hardened test specimen and taking the hardness readings here. The test specimen of the analysis to be tested is heated to the temperature above the critical range atv which it will be hardened in production and cooled by extracting heat :from one end face only to harden the specimen as above described.

Various changes and modiiications of the embodiment of my invention specifically described herein may be made without departing from the 3 providing an elongated test specimen of the analysis to be tested, heating said test specimen above the critical temperature of the steel to a hardening temperature, cooling said test specimen by spraying cooling Water at substantially a constant temperature onto one end face only of said test specimen and measuring the hardness of the cooled specimen at points along its length.

3. The method of determining the hardness characteristics of a steel which comprises, providing an elongated test specimen of the analysis to be tested, heating said test specimen above the critical temperature of the steel to a hardening temperature, rapidly transferring said heated test specimen and supporting the same above and in spaced relation to a nozzle, forcing a jet of water through said nozzle and into contact with one end face only of the heated test specimen to cool the specimen and measuring the hardness of the cooled specimen at various points along its length.

4. The cooling step in a method of determining the hardness characteristics of a steel test specimen which comprises, supporting an elongated test specimen heated to a temperature above the critical temperature of the steel in a fixture in spaced relation to a nozzle and forcing cooling water at substantially a constant temperature through said nozzle into contact with one end face only of the heated test specimen to harden the test specimen by cooling the same from one end only.

5. In an apparatus for cooling a steel test specimen which has been heated to a temperature above the critical temperature of the steel for determining the hardness characteristics of the steel, a tank for holding a supply of cooling water, a nozzle, a fixture for supporting an elongated test specimen which has been heated to a temperature above the critical temperature of the steel in spaced relation to the nozzle and above the level of the water supply in said tank and means for pumping water from the tank through the nozzle and into contact with one end face only of the heated test specimen to harden the same by cooling from one end only.

WALTER E. J OMINY. 

